From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A3826C43331 for ; Mon, 30 Mar 2020 14:07:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76C1120776 for ; Mon, 30 Mar 2020 14:07:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="l09D8veP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728490AbgC3OHP (ORCPT ); Mon, 30 Mar 2020 10:07:15 -0400 Received: from mail-wm1-f66.google.com ([209.85.128.66]:38129 "EHLO mail-wm1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725268AbgC3OHP (ORCPT ); Mon, 30 Mar 2020 10:07:15 -0400 Received: by mail-wm1-f66.google.com with SMTP id f6so15466477wmj.3; Mon, 30 Mar 2020 07:07:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:reply-to:references:mime-version :content-disposition:in-reply-to:user-agent; bh=NkzDxDJV1bnIzEyyQHH60q1JMe3S2qaalEpyevgeDjU=; b=l09D8vePmsTy6YJfx5OBWOTZXcDmZP5AqjJZZ2/1V3JxhHYaHl0Ng7dBXXkGqvkbNO 70Gny56xP33iDCFXLwqULkq+3yPJva9Ww7Zdd8Ud2P7Gl5mvKuT+WXIQW/eGwOW5uthm zxw4Dm10afQz6D2RrJbiELMAeI1+bHF32zI8K9wEwL9dgvy452c/UeATCmoOeyG1QwTQ wKasux9fjj7o0Ws3dHATmouJhcROWFRLaPwolcR5qYqd7RcLsmFGDsICAQHN2JIo/DMH DFre0geNYld5cX4Kzxj8bSNs8iYyKDext4OttK9wmN5UQyxn1fDhEvLZxESD9C0fEcDZ ANNg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:reply-to :references:mime-version:content-disposition:in-reply-to:user-agent; bh=NkzDxDJV1bnIzEyyQHH60q1JMe3S2qaalEpyevgeDjU=; b=tJqlxP1PmW2LzdAyn77F0pQtuXE7yw66CbIKDB7rtHUFvhQ9ZOzf8agJ2wsULFyuwi jTU2tvVglWEFgVGAvyVxCVcQ1pS171BhKwa1Eu1v93E4CtKCz+O5S9Z6/+TprcwBEvsM /qhN56ciJL4SIN4AulpxlRtT1nbJqh1Du32UW0kBehsAtWCgDoXH9yazQjkozl2tnUPE TXeB06KibDqXV02Xp11c+aDRgzXsWzF2ajLYyeEt/qgbpTTxlr/nytBmAIt6OjdAy8Sx //Q2NqHvcfkWy1h7VhX7qv9cDSzyFnT8A2WAnyzL3Gh7MaWngw+dm8m2Ug46M0uULnQJ Po2w== X-Gm-Message-State: ANhLgQ2e7nAEuxgeREKDxG5ZygFdAlzKvLqupZk09ds8Nm5bsdfA4L8w kFpY8gja4Ue2plc2NPV0TeI= X-Google-Smtp-Source: ADFU+vvDgfqqnHf5IRDG0vNghnouBgCUY5+ARj5KVNJUOS4CEX51oW7b0ZiqGVsrAZGVOvfw235vGA== X-Received: by 2002:a1c:8108:: with SMTP id c8mr13124272wmd.50.1585577233309; Mon, 30 Mar 2020 07:07:13 -0700 (PDT) Received: from localhost ([185.92.221.13]) by smtp.gmail.com with ESMTPSA id b203sm21270063wmc.45.2020.03.30.07.07.12 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 30 Mar 2020 07:07:12 -0700 (PDT) Date: Mon, 30 Mar 2020 14:07:12 +0000 From: Wei Yang To: Matthew Wilcox Cc: Wei Yang , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/9] XArray: simplify the calculation of shift Message-ID: <20200330140712.sloduuoqc5jid64m@master> Reply-To: Wei Yang References: <20200330123643.17120-1-richard.weiyang@gmail.com> <20200330123643.17120-3-richard.weiyang@gmail.com> <20200330132028.GA22483@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200330132028.GA22483@bombadil.infradead.org> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 30, 2020 at 06:20:28AM -0700, Matthew Wilcox wrote: >On Mon, Mar 30, 2020 at 12:36:36PM +0000, Wei Yang wrote: >> When head is NULL, shift is calculated from max. Currently we use a loop >> to detect how many XA_CHUNK_SHIFT is need to cover max. >> >> To achieve this, we can get number of bits max expands and round it up >> to XA_CHUNK_SHIFT. >> >> Signed-off-by: Wei Yang >> --- >> lib/xarray.c | 6 +----- >> 1 file changed, 1 insertion(+), 5 deletions(-) >> >> diff --git a/lib/xarray.c b/lib/xarray.c >> index 1d9fab7db8da..6454cf3f5b4c 100644 >> --- a/lib/xarray.c >> +++ b/lib/xarray.c >> @@ -560,11 +560,7 @@ static int xas_expand(struct xa_state *xas, void *head) >> unsigned long max = xas_max(xas); >> >> if (!head) { >> - if (max == 0) >> - return 0; >> - while ((max >> shift) >= XA_CHUNK_SIZE) >> - shift += XA_CHUNK_SHIFT; >> - return shift + XA_CHUNK_SHIFT; >> + return roundup(fls_long(max), XA_CHUNK_SHIFT); > >This doesn't give the same number. Did you test this? > >Consider max = 64. The current code does: > >shift = 0; >64 >> 0 >= 64 (true) >shift += 6; >64 >> 6 < 64 >return 12 > >Your replacement does: > >fls_long(64) = 6 fls_long(64) = 7 >roundup(6, 6) is 6. > >Please be more careful. -- Wei Yang Help you, Help me